Unsymmetrical esters of 1,4-dihydropyridine-dicarboxylic acids, processes for their production and their use as coronary and antihypertensive agents are disclosed in U.S. Pat. No. 3,799,934. U.S. Pat. No. 3,932,645 includes the mixture of nimodipine and an inert carrier and the use of the compound to effect coronary vascular dilatation. Additionally, it has been found that nimodipine has an advantageous action on cerebral circulatory disturbances. U.S. Pat. No. 4,406,906 discloses a method of combating pathologically reduced cerebral functions and performance weaknesses, cerebral insufficiency and disorders in cerebral circulation and metabolism.
Nimodipine has been the subject of considerable investigation. Studies conducted by Harper et al, J. Cereb. Blood Flow Metab., 1: 49-356, 1981 indicated that nimodipine crosses the blood-brain barrier. The dilatory effects of nimodipine are known to be more selective to the cerebral vessels than hydralazine. Harris et al, Stroke 13: 759-766, 1982); Kazda and Towart, Acta Neurochirurgica, 63: 259-265, 1982; Towart et al, Arzneimittelforsch, 32: 338-346, 1982. Further, nimodipine exerts a cerebral vasodilatory effect without increasing intracranial pressure. Hadley et al, J. Neurosurg., 66: 387-393, 1987.
Under appropriate circumstances, embryonic CNS tissue readily survives transplantation into the adult brain (Azmitia, E. C. and A. Bjorklund, Eds. 1987, Cell and Tissue Transplantation into the Adult Brain, Ann. N.Y. Acad. Sci., 495; Bjorklund, A., and U. Stenevi, Eds. 1985, Neural Grafting in the Mammalian CNS, Elsevier, Amsterdam). The conditions for viable transplantation involve several factors, including the age and developmental status of the donor tissue and the suitability of the host transplantation site.
The optimal developmental status of the donor tissue appears to be related to the few days in embryonic development after the stage of final cell division of the particular group of neurons under investigation (Das, G. D., et al, 1980, Am. J. Anat. 158: 135-145; Olson, L., et al, 1983, Pages 407-442 in S. Federoff, Ed. Advances in Cellular Neurology, Vol. 4, Academic Press, New York; Seiger, A., 1985, Pages 71-77 in A. Bjorklund and U. Stenevi, Eds., Neural Grafting in the Mammalian CNS, Elsevier, Amsterdam). For mesencephalic dopamine cell suspension grafts in rats, the optimal age for transplantation is around Embryonic Day 14 (E14; crown-rump length, CRL, 11-14 mm), and by E16-E17 (CRL, 16-20 mm) only poor survival is obtained (Bjorklund, A., et al, Cell Tissue Res., 212: 39-45; Brundin, P., et al, 1988, Dev. Brain Res., 39: 233-243; Dunnett, S. B., et al, Brain Res., 415: 63-78). Moreover, graft survival is optimal when made within 1-3 hours of embryonic dissection, unless the cells to be transplanted are cryopreserved or maintained in culture (Brundin, P. et al, 1988, ibid; Das, G. D., et al, 1983, J. Neurosci., Methods 8: 1-15; Gage, F. H., et al 198, Neurosci. Lett., 60: 133-137). For example, Brundin et al, 1985, Brain Res., 331: 251-259, used vital cell stains to characterize the viability of graft cells in suspension and found that the viability of embryonic dopamine neurons declined dramatically 3- 6 hours after dissection and preparation.
Another factor important for graft survival is the provision of a suitable transplantation site in the host brain with adequate vascularization to nurture the newly implanted tissue. This is particularly important for grafts of "solid" tissue pieces (Stenevi, U., et al, 1976, Brain Res., 114: 1-20), but has been thought to be less critical for suspension grafts. Thus, Lawrence et al (1984, Neuro-science, 12: 745-760) observed that fragile host blood vessels begin to grow into hippocampal grafts within 24 hours of transplantation, and within the first week considerable growth of both wide-diameter reactive vessels and dilated thin-walled marginal vessels gives rise to many small capillaries invading the transplant. Smith and Ebner (1986, The differentiation of non-neural elements in neocortical transplants, pages 81-101 in G. D. Das and R. B. Wallace, Eds., Neural Transplantation Research, Springer, N.Y.) and Rosenstein (1987, Science, 235: 772-774) also observed a substantial growth of blood vessels into neocortical transplants, but emphasized that the vessels appear to retain immature properties, such as relative permeability to circulating proteins. Rosenstein (ibid) hypothesized that an incomplete blood-brain barrier may serve to promote graft survival by permitting exposure of the fetal cells to blood-borne growth factors derived from the host brain.
Nimodipine, (isopropyl(2-methoxyethyl)14-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-py ridine dicarboxylate) is a dihydropyridine which acts as a calcium channel antagonist (Betz, E., et al, Eds. 1985, Nimodipine: Pharmacological and Clinical Properties, Schattauer, Stuttgart; Harris, R. J., et al 1982, Stroke, 13: 759-766). This drug selectively dilates cerebral blood vessels and increases cerebral blood flow without a concomitant effect on systemic arterial pressure (Towart, R., et al, 1985, Effects of the calcium antagonist nimodipine on isolated cerebral vessels, pages 207-215; and Kazda, S., et al, 1985, Prevention of acute and chronic cerebrovascular damage with nimodipine in animal experiments, pages 31-43, both in E. Betz, K. Deck and F. Hoffmeister, Eds., Nimodipine: Pharmacological and Clinical Properties, Schattauer, Stuttgart). Nimodipine appears to be especially potent in areas with inadequate circulation (Harper, A. M., 1985, Effect of a dihydropyridine-type calcium antagonist of cerebral blood flow and metabolism, in A. Flechenstein, C. Van Breemen, R. Gross and F. Hoffmeister Eds., Cardiovascular Effect of Dihydropyridine-Type Calcium Antagonists and Agonists, Springer, Berlin; Mohamed, A. A., et al, 1985, The effect of nimodipine on local cerebral blood flow, glucose use and focal cerebral ischemia using acute autoradiographic techniques, pages 105-112 in E. Betz, K. Deck and F. Hoffmeister, Eds., Nimodipine: Pharmacological and Clinical Properties, Schattauer, Stuttgart). These properties of nimodipine have led to it being used clinically to enhance blood flow in migraine and cluster headaches and to treat certain types of ischemic brain insult (Dorn, M., 1985, Effect of nimodipine on the well-being, symptoms and efficiency of ambulatory patients with cerebrovascular disorders, pages 295-304; Held, K., et al, 1985, Efficacy and tolerability of nimodipine in patients with old-age cerebrovascular dysfunction, pages 289-292; Menazzi, D., et al, 1985, Nimodipine in the treatment of chronic cerebrovascular insufficiency, pages 329-331; and Mikus, P., et al, 1985, Nimodipine, a centrally active calcium antagonist, Results of a clinicopsychometric study, pages 329-331, all in E. Betz, K. Deck, and F. Hoffmeister, Eds., Nimodipine: Pharmacological and Clinical Properties, Schattauer, Stuttgart).
The present study was designed to test the hypothesis that nimodipine might also increase the viability of neural transplants by enhancing vascularization of the grafts. The results of this study were published by Finger and Dunnett in Experimental Neurology, 104, 1-9, 1989. Transplantation of embryonic ventral mesencephalic cells into the neostriatum of rats with unilateral dopamine-depleting lesions was chosen as the model system for investigation. The effects of nimodipine on the survival, growth, and vascularization of the grafts were considered, both under optimal transplantation conditions and using tissue considered suboptimal either by virtue of older donor age or by maintaining the cells for several hours at room temperature prior to transplantation.